linux-kernel - Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from

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Message-ID: <20191107154341.GX3622521@devbig004.ftw2.facebook.com>
Date:   Thu, 7 Nov 2019 07:43:41 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: memcg: switch to css_tryget() in
 get_mem_cgroup_from_mm()

Hello,

On Thu, Nov 07, 2019 at 01:21:25PM +0100, Michal Hocko wrote:
> Hmm, how can we have a task in an offline memcg? I thought that any
> existing task will prevent cgroup removal from proceeding. Is this some
> sort of race where the task managed to disassociate from the cgroup
> while there is still a binding to a memcg existing? What am I missing?

The previous cgroup one was from bsd process accounting which happens
after the process is marked head.  This one IIUC is from core dumping
path.

Thanks.

-- 
tejun